The present invention relates to a magnetic tape cassette, and more particularly to an improved magnetic tape cassette for video use.
Conventionally, various types of video magnetic tape cassettes have been employed. Recently, video tape cassettes of higher performance with respect to a picture quality, etc., have been desired. Also, in view of current diverse needs, the numbers of the available types kinds of video cassettes has shown a tendency to increase.
In view of such circumstances, a tape cassette commonly referred to as a ".beta. cam cassette" and a video tape cassette commonly referred to as a ".beta. cam SP cassette" have been marketed. The two cassettes are quite similar to each other, differing only in the material of the magnetic tape, the construction of a detection hole formed in the bottom face of the cassette for identifying the type of cassette, and a construction for preventing mistake erasure. Otherwise, the casings of the two cassettes are totally the same.
The mold used for molding the cassette casings is relatively complicated and costly, and therefore it has been common practice to manufacture the two cassette casings using the same mold since it is not desirable, from the viewpoints of productivity and cost, to use two different molds when there are only very minor differences between the two types of cassettes.
However, cassettes manufactured using the same mold have suffered from deficiencies due to the difference in the mistake erasure prevention construction. This difference will be described.
In the mistake erasure prevention construction of the .beta. cam cassette, as shown in FIG. 4, a snap-off tab 30 is provided on the bottom face 11 of the cassette at a position close to the front in the vicinity of one side face 12 of the cassette. As is well known, with this construction, if the tab 30 remains extant, rerecording can freely be carried out repeatedly, while if the tab 30 is snapped off, rerecording cannot be effected. After the tab 30 is snapped off, there remains a concave portion surrounded by walls, which concave portion does not communicate with an inside of the cassette body.
On the other hand, the mistake erasure prevention construction of the .beta. cam SP cassette is provided at the opposite position with respect to the position of the tab 30 of the .beta. cam cassette with respect to the left-and-right direction of the cassette. Specifically, in the mistake erasure prevention construction of the .beta. cam SP cassette, an upward-and-downward slidable movable plug 40 (sliding in the direction of the thickness of the cassette) is mounted in an insertion hole 14 formed in the bottom face 11 of the cassette, as shown in FIG. 5. Leg portions 5, etc., of the movable plug 40 are resiliently engaged with inner walls of the insertion hole 14, and retainer portions 3 and 4 constituted by part of the leg portions 5 are engaged with a retainer aperture 16 and a distal edge 17 of the inner wall, respectively. When the movable plug is retained so as to lie flush with the bottom face 11 of the cassette, rerecording is enabled. Also, by manipulating a thumbpiece 41, exposed through a notch 15, downward in FIG. 5 (in the direction of an arrow B) such as with a finger movement, the retainer portion 3 can be retained by an engaging portion (not shown) in such a manner that the insertion hole 14 defines a recess so as to disable rerecording. The insertion hole 14 is communicated with the inside of the cassette body in order to permit the movable plug 40 to move upwardly and downwardly.
When cassette casings are manufactured using a mold which is capable of accommodating both types of mistake erasure prevention constructions separately at left and right sides of the casing described above, in the case that the cassette casing is employed as a .beta. cam SP cassette, no problem is encountered by arranging the mold in such a manner that the tab 30 shown in FIG. 4 is removed beforehand while the movable plug 40 is mounted in the insertion hole 14 as shown in FIG. 5. However, in the case of the .beta. cam cassette, when it is shipped with the movable plug 40 of FIG. 5 attached for acting as a dustproof device while remaining the tab 30, which plug performs no actual function as a mistake erasure preventing device, there has been encountered the disadvantage that the user sometimes mistakenly attempts to operate the movable plug 40 to control rerecording although he should snap the tab 30 off, since the cassette is shipped with the movable plug 40 which can readily be operated. Thus, the user may not attain the correct operation for the erasure preventing. On the other hand, if the movable plug 40 is removed in order to avoid the above-described problem that the user mistakenly operates the movable plug 40 as he thinks that it acts as an erasure preventing device, there has arisen the problem that dust or other foreign matter may enter the cassette since the insertion hole 14 is in communication with the interior of the cassette.